and the latter get a free meal. When a wrasse tends a great grouper, the little cleaner sometimes swims into the gill chambers and mouth, demonstrating remarkable faith that it is not going to be eaten. When the grouper wants to depart, it tells its cleaner that it wants to go by closing its mouth a little and shaking its body. It does this even when it is in danger of being attacked. A safer way to proceed would be to gulp down the cleaner and leave immediately. The first strategy would be a form of cooperation, the second a form of defection.
The nuisance of parasites—ticks—has led to the emergence of another instance of this mechanism at work, in the form of reciprocal grooming, this time among impala, a kind of antelope found in Africa. And when it comes to our closest relatives, textbooks are crammed with examples. One was reported in 1977 by Craig Packer in the Gombe Stream Research Centre, Tanzania, where there has been a long-term study of olive baboons, so named because of their distinctive fur. Packer, now at the University of Minnesota, reported how one male will help another who had previously come to his aid in ganging up on more senior baboons, so that one of them can have sex with the senior’s female. Even though the helper will not have sex immediately after forming a coalition, he still cooperates because he expects the favor will be returned.
Sri Lankan macaques Macaca sinica will tend the wounds of a fellow male in order to secure the latter macaque’s support in future conflicts. Unsurprisingly, juvenile males are especially attentive to the injuries of hefty adults, who can provide more muscle in a future fracas. One study of macaques in Kalimantan Tengah, Indonesia, went so far as to suggest that males were more likely to mate with females that they have previously groomed, the grooming being a kind of payment for sex, a finding given the colorful interpretation that the “oldest profession”—prostitution—seems to date back long before humans.
Male chimpanzees share meat to bind social alliances, and there is some evidence that they increase the degree to which they cooperate in line with how much a partner has been helpful toward them. Reciprocity can be exchanged in all kinds of currencies, such as grooming, support in fights, babysitting, warning, teaching, sex, and of course food. Frans de Waal of Emory University, Atlanta, observed how a top male chimpanzee, Socko, had more chance of obtaining a treat from his fellow chimp May if he had groomed her earlier that day.
There are caveats, however. One is that different scientists use terms such as reciprocity in various ways. Another is that, when it comes to observing behaviors in the wild, it can take many lengthy and detailed studies to understand what is really going on. Tim Clutton-Brock, a professor of ecology and evolutionary biology at Cambridge University, says that it can be hard to sift concrete examples of reciprocity from the illusory ones that can be explained another way.
Let’s take Craig Packer’s inspirational olive baboon research, for example. Packer had originally thought that the males were trading favors in their pursuit of sex. His original argument went that the allies switch roles, so that each one benefits from the association. But follow-up studies suggested that the cooperating males actually compete with each other when it comes to snatching the prize. The only way they can have an opportunity to mate is to join forces and to cooperate, true enough. But once the existing consort is driven off, then it is every man for himself when it comes to getting the girl. Packer puts it like this: “In this scenario, cooperation is like a lottery, and you can’t win if you don’t buy a ticket. Because two against one gives very good odds of success, the price of the ticket is very low compared to the value of the prize. Participate in enough lotteries of this sort, and you will always come out ahead—and so will your partners.”
RECIPROCITY RULES
Oliver: I remember you!
Grocer: And I remember you too. Now get out of my store and stay out!
Oliver: Oh, don’t be like that. Let bygones be bygones. Let’s help each other. You have a business, and we have a business. We’ll send people to your store, and you send people to our store. What do you say?
Grocer: You mind your business and I’ll mind my business. Now get out before I throw you out!
—Laurel and Hardy in Tit for Tat
One way to determine which examples of direct reciprocity are real is to think about the qualities that are necessary for this mechanism to work. The evolution of cooperation by direct reciprocity requires that players recognize their present partner and remember the outcome of previous encounters with him or her. They need some memory to remember what another creature has done to them, and a little bit of brainpower to figure out whether to reciprocate. In other words, direct reciprocity requires reasonably advanced cognitive abilities.
I am sure that enough cognitive capacity is available in certain species of birds and among our closer relatives, most certainly the great apes. I am certain there is enough grey matter when it comes to human beings. If Harry does Fred a favor, Fred can remember what Harry looks like. He can also remember his good deed and how Harry has behaved in the past. Fred certainly has sufficient cognitive capacity to figure out from what he can remember if Harry is trustworthy and then tailor his behavior accordingly.
When it comes to the soap opera of everyday life, examples of direct reciprocity are everywhere. The running of a household depends on a ceaseless, mostly unconscious bartering of goods and services. In the kitchen, the one who cooks is often spared the drudgery of the washing up and vice versa. The concord among the members of a student house depends on everyone contributing equitably to cleaning duties, a food kitty, or whatever. If a friend helps us to move house, there is an obligation on us to help to pack his furniture when it is time for him to move, or unpack his crates. Families often harbor expectations that children will reciprocate for the care they receive as babies and as children by looking after their elderly parents.
When we receive invitations to dinner, a night at the theater, and so on, there comes an unwritten obligation to reciprocate in some way, in kind or with a treat in return. If a colleague at work hands you a gift-wrapped present, you make a mental note to reciprocate when her birthday comes around. When someone holds open a door, or gestures toward the mountain of food in a buffet, and says, “After you,” many instantly reply, “No, you go first.” The same sense of duty to reciprocate helps to make the ritual gift giving at Christmas expensive. And it can be found in bigger tribes and groups of people: businesses may have long-term contractual obligations with each other; governments make treaties with one another; and so on and so forth.
We repay meanness in the same coin. This is best reflected in the phrase “an eye for an eye, a tooth for a tooth,” from Exodus 21:24–27, in which a person who has taken the eye of another in a fight is instructed to give equitable recompense—his own. In the code of Hammurabi, created by an ancient Babylonian king, the principle of reciprocity is expressed in exactly the same way (“If a man put out the eye of another man, his eye shall be put out” and “If a man knocks the teeth out of another man, his own teeth will be knocked out”). One can see the same tit-for-tat logic in the idea of a “just war,” where the methods used to prosecute a conflict are proportionate to a given threat.
Unsurprisingly, given its central role in human life, reciprocity has inspired comedy. The vintage duo Laurel and Hardy used acts of slapstick revenge to give their movies a satisfying climax. One of their short films released in 1935 revolves entirely around reciprocal retaliations. Appropriately enough, the film is titled Tit for Tat.
So there’s plenty of evidence that we live in a reciprocating world. But, of course, it does not always follow that another player in the game of life will reciprocate. Because there is a cost involved in helping another, cooperation always comes with the threat of exploitation. Why should anyone share in hard work or return a favor? Why not cheat? Why not let the other guy toil and sweat, so you can reap the rewards of his hard
